When to Use or Avoid Donut Charts

Background

Now that Krispy Kreme donuts have made the transatlantic hop and permeated British breakfast culture, sales managers from Glasgow to Southampton are able to top-up their sugar levels before hitting the sales floor with a sugary smile on their face!

Meanwhile, in the dimly lit wee hours of the morning, some statistically minded sales managers are attempting to boldly go where few managers have gone before. They're using donut charts on their sales team dashboards, instead of pie charts, bar charts or other tried and true approaches.

Why are pie and donut charts used?

Pie and donut charts are used because they allow comparison of each segment against the whole. In other words, if there are 4 slices, it lets you easily see how much slice A, B, C and D contributes to the whole, and are often represented as percentages rather than amounts.

Pie and donut charts are used to compare segments against the whole, not one another.

Examples of donut and pie charts

What are their weaknesses?

In pie charts, users rely on the inner or center angle plus outer arc to estimate the relative size. However, in donut charts that inner section has been removed and hence makes it more difficult to do because it relies on using the naked eye to measure or guess the length of the arc (outer perimeter).

Pie charts rely on inner angle and outer arc for judging sizes. Donut charts rely on eyeballing the length of only outer arcs, which is more difficult.

What other weaknesses are there?

Adding a legend actually makes a donut chart harder to use, since you have to keep glancing back and forth between the donut and the legend to know what colour represents what region. This is why legends are not useful in pie and donut types of charts.

3D styling of donut charts can render them nearly impossible to read and try to make sense.

Do not use a legend or 3D styling, as they make the charts harder to read.

Why are donut charts used over pie charts?

Donut charts are sometimes used over pie charts because they can tell the same story as pie charts while taking up less space, thanks to the missing middle section (which sometimes is used for additional labels or data). Also, donut charts are often viewed as more attractive than pie charts, and are usually selected for their good looks.

Donut charts work better when space is limited and their size must be smaller in order to fit. They're also prettier.

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Bottom Line:

Donut charts can be preferred to pie charts, when space is limited or when prettiness is desired over pure readability, but should not be used as 3D or with legends. Both donut and pie charts are great for comparing a select few items against the whole, but are poor at comparing many elements or comparing element to element directly.

• Use donut charts if you want beauty over usability or you only have limited space and a few segments to include.
• Avoid legends and 3D styling with both.
• For comparing segments to one another, switch to a bar chart.
• Donut charts are the pretty favourite and make a good breakfast too!